By studying the brain in live and behaving subjects, we obtain fundamental insight into the neural basis of natural behaviors. Such basic biology research is essential as the fundamental underpinning forunderstanding brain function when compromised by disease or injury. In this proposal we will investigate the brain mechanisms for modulating the flow of sensory information to the cerebral cortex, where perception occurs. With only minor exceptions, all sensory signals are relayed to cortex through a brain structure called the thalamus. Other parts of the brain modulate thalamic throughput by specific kinds of projections or neurotransmitters. Depending on the "tone" of these various inputs, the thalamus switches between two different modes ofrelay. Onemoderelays sensory information very faithfully; whereas, the other distorts or disconnects the relayed information. The faithful "tonic mode" predominates during wakefulness and the other "burst mode" predominates during deep sleep. The nature of the transition between these two modes in the living animal is currently not well understood, and will be investigated here. A major source of influence for this state-related tone comes from abrainstem structure called the parabrachial region (PER) that uses the special neurotransmitter acetylcholine. In order to understand this "gate keeper" action better, we intend to manipulate the activityin the PBR experimentally while observing the effect in the visual relay nucleus of the thalamus, the lateral geniculate nucleus (LGN). Essentially, we will use the visual system to understand how the PBR "arouses"the thalamus. The health relatedness ofthis research is that study of how the normal, healthy brain works is how we come to understand the human condition in health and in illness.